Automatic recognition of radar scan type

ABSTRACT

A system for determining the scan type of a signal, such as a radar signal, includes a scan detector, a transformer (e.g., an FFT algorithm), a correlator, and a decision block. The signal is received and processed by the scan detector. The scan detector provides an envelope signal, representing the scan type of the received signal. The envelope signal is transformed, typically from a time domain signal to a frequency domain signal, by any of several processes including a Fourier transform, a Laplace transform, an FFT, or a DFT. The transformed envelope signal is compared to several scan data sets by the correlator. Each scan data set represents a particular scan type. If the decision block determines that the comparison between the transformed envelope signal and a scan data set meets (or exceeds) a degree of similarity, the scan type of the received signal is determined to be the scan type of that scan data set.

FIELD OF THE INVENTION

[0001] This invention relates generally to radar detection,identification, and warning systems, and more particularly to a systemand method for automatically determining radar scan type.

BACKGROUND OF THE INVENTION

[0002] Many radar systems search, or scan, a spatial region to detectand track targets of interest. Typically, radar systems transmit energyat a specific transmission frequency (carrier frequency) or set oftransmission frequencies. Detected frequency, time, and amplitudecharacteristics of radar signals are typically used to identify the typeof transmitter used to transmit the received signals. Often inferredfrom these characteristics are the type of weapon system associated withthe transmitter, and the present operational mode (e.g., search, track,missile-in-flight). Present techniques used to classify and identify thereceived radar signals rely primarily on the measured carrier frequencyparameters, frequency modulation type parameters, and time domainmodulation parameters such as pulse width and pulse repetition interval,and scan type, often inferred from the more easily determined scanperiod.

[0003] However, many radar types that perform the same functions, suchas search or fire control, have parameter domains that overlap. Scantype is an important parameter for resolving these ambiguities, and fordetermining the mode of an associated weapons system. The scan typeindicates the type of scanning technique being used by a radar system,for example, conical scan or circular scan. Historically, scan typecould only be determined by a human operator (usually present on largeor dedicated signal collection platforms, but rarely present on combatplatforms, and never on weapons or remotely piloted vehicles), listeningto the scan modulation. Typically, the operator would listen for severalscan periods, and even then the analysis was subject to humaninterpretation. This analysis requires an experienced operator, whoseactions and analyses are of course, subject to human error. Thelikelihood of such errors or mistakes may be further increased when theoperator must perform in the heat of battle or under other crisisconditions. Current automatic classification systems only infer likelyscan type or types from scan rate. Scan rate is the rate at which thetransmitted radar pulse is received by the receiving radar system. Theanalysis performed by these systems is often ambiguous and, because theidentification of scan type is inferred from measured scan period, theinference itself can be wrong. Therefore, there is a need for a fast,repeatable, highly accurate mechanism for the automated determination ofscan type as an aid to identifying radar types and modes, that does notsuffer the above disadvantages.

[0004] Energy received at an unintended receiver (the target or acollection system, at a location other than the transmitter's receiver),also includes the signal amplitude envelope, modulated in accordancewith the type of scan used by the transmitting radar system. Knowledgeof the scan type can aid an operator (e.g., a pilot of a targetedaircraft, or an electronics warfare operator) in determining the type ofradar transmission system, such as, for example ground base radar,airborne radar, or missile radar, and the mode of the associated weaponssystem (search, acquisition, track, missile guidance).

SUMMARY OF THE INVENTION

[0005] A system and method for determining a scan type of a signalinclude a scan detector for receiving a signal and providing an envelopesignal. The envelope signal is indicative of the scan type of thesignal. The envelope signal is transformed. A correlator compares thetransformed envelope signal with at least one predetermined data set,wherein each predetermined data set corresponds to one of a plurality ofscan types. The scan type of the signal is determined by a decisionblock in accordance with a degree of similarity between each of thepredetermined data sets and the transformed envelope signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The foregoing and other objects, aspects and advantages will bebetter understood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

[0007]FIG. 1A is a time domain plot of the envelope of a steady scanrecognizable by a scan recognition system in accordance with the presentinvention;

[0008]FIG. 1B is a time domain plot of the envelope of a conical scanrecognizable by a scan recognition system in accordance with the presentinvention;

[0009]FIG. 1C is a time domain plot of the envelope of a circular scanrecognizable by a scan recognition system in accordance with the presentinvention;

[0010]FIG. 1D is a time domain plot of the envelope of a helical scanrecognizable by a scan recognition system in accordance with the presentinvention;

[0011]FIG. 1E is a time domain plot of the envelope of a lobe switching,or sequential lobing, recognizable by a scan recognition system inaccordance with the present invention;

[0012]FIG. 1F is a time domain plot of the envelope of a unidirectionalsector scan recognizable by a scan recognition system in accordance withthe present invention;

[0013]FIG. 1G is a time domain plot of the envelope of a bi-directionalsector scan recognizable by a scan recognition system in accordance withthe present invention;

[0014]FIG. 1H is a time domain plot of the envelope of a circular rasterscan recognizable by a scan recognition system in accordance with thepresent invention;

[0015]FIG. 1I is a time domain plot of the envelope of a unidirectionalraster scan recognizable by a scan recognition system in accordance withthe present invention;

[0016]FIG. 1J is a time domain plot of the envelope of a bi-directionalraster scan recognizable by a scan recognition system in accordance withthe present invention;

[0017]FIG. 1K is a time domain plot of the envelope of a spiral scanrecognizable by a scan recognition system in accordance with the presentinvention;

[0018]FIG. 1L is a time domain plot of the envelope of a Palmer circularscan recognizable by a scan recognition system in accordance with thepresent invention;

[0019]FIG. 1M is a time domain plot of the envelope of a Palmerunidirectional scan recognizable by a scan recognition system inaccordance with the present invention;

[0020]FIG. 1N is a time domain plot of the envelope of a Palmerbi-directional scan recognizable by a scan recognition system inaccordance with the present invention;

[0021]FIG. 1P is a time domain plot of the envelope of a true rasterscan recognizable by a scan recognition system in accordance with thepresent invention;

[0022]FIG. 1Q is a time domain plot of the envelope of a Palmer rasterscan recognizable by a scan recognition system in accordance with thepresent invention;

[0023]FIG. 2 is a functional block diagram of an exemplary automaticscan type recognition system 200 in accordance with the presentinvention;

[0024]FIG. 3 is a functional block diagram of an exemplary scan detectorin accordance with an embodiment of the present invention;

[0025]FIG. 4 is a flow diagram of an exemplary process to automaticallydetermine a scan type in accordance with an embodiment of the invention;and

[0026]FIG. 5 is a block diagram of a receiving platform comprising anantenna and a computer processor, in accordance with an exemplaryembodiment of the invention.

DETAILED DESCRIPTION

[0027] Many radar systems search, or scan, a spatial region to detectand/or track targets of interest. Typically, radar systems transmitenergy at a specific transmission frequency (carrier frequency) or setof transmission frequencies. Energy received by a receiving platform,comprises the transmitted energy, which is amplitude modulated inaccordance with the type of scan used by the transmitting radar system.Knowing the scan type can aid an operator (e.g., an electronics warfareoperator, or a pilot of a targeted aircraft) in determining the type ofradar transmission system, such as, for example ground base radar,airborne radar, missile radar, and/or the radar mode. A scan recognitionsystem in accordance with the present invention determines the type ofscan being employed by the transmitting radar system. As described,herein scan type is determined from the scan envelope and is notdependent upon radar frequency, frequency modulation, pulse width, pulserepetition rate, or scan rate.

[0028] Various scanning techniques are employed by existing systems. Inan exemplary embodiment of the invention, received energy is demodulatedto provide an envelope signal representing the scan type. FIGS. 1Athrough 1Q are time domain plots of various types of radar scan envelopesignals, over a single scan period, recognizable by a scan recognitionsystem in accordance with the present invention.

[0029]FIG. 1A is a time domain plot of the envelope of a steady scan. Asteady scan is the result of a transmitter emanating radiation with noapparent scanning of the transmitting attenna. A steady scan mayindicate that the transmitter is part of a tracking radar, in a tighttrack, or other type of scan that has “locked in” on the receivingplatform. A steady scan envelope is typically indicates that thereceiving platform is being tracked, and is thus given high priority.

[0030]FIG. 1B is a time domain plot of the envelope of a conical scan. Aconical scan is a continuous two-dimensional scan, in azimuth (az) andelevation (el), resulting in a sinusoidal modulation of the receivedcarrier frequency, as long as the receiving platform is not beingtightly tracked. As the receiving platform stays within the mainlobe ofthe transmitting radar's beam pattern, no sidelobes or otherdistinguishing features are noticeable in the envelope signal.

[0031]FIG. 1C is a time domain plot of the envelope of a circular scan.A circular scan is a continuous one-dimensional scan in azimuthresulting in modulation of the received carrier frequency showing thelobe structure of the antenna pattern of the transmitting radar system,including the mainlobe 40, sidelobes 42, and back lobe 44 (the energyreceived by the receiving platform when the mainlobe of the radar systemis steered in a direction approximately 180° away from the receivingplatform.

[0032]FIG. 1D is a time domain plot of the envelope of a helical scan. Ahelical scan is a continuous two-dimensional scan comprising a circularscan in azimuth superimposed on a slower linear scan in elevation. Atthe receiving platform, the modulation appears as a sequential circularscan, wherein the average received signal strength increases anddecreases in a step like manner. As the mainlobe of the transmitted beampattern approaches the elevation of the receiving platform, the signalstrength increases (as shown by arrow 46). As the mainlobe of thetransmitted beam pattern passes through the receiving platform'selevation and continues to higher elevations, the signal strengthdecreases (as shown by arrow 48).

[0033]FIG. 1E is a time domain plot of the envelope of lobe switching,or sequential lobing. Lobe switching is a continuous two-dimensionalscan in azimuth and elevation resulting in a square wave modulation ofthe carrier frequency. As the receiving platform remains within themainlobe of the beam pattern of the transmitting radar system, no sidelobes or other distinguishing features of the transmitting radarsystem's antenna pattern are apparent.

[0034]FIG. 1F is a time domain plot of the envelope of a unidirectionalsector scan. A unidirectional sector scan is a discontinuousone-dimensional scan in azimuth resulting in modulation of the receivedcarrier frequency displaying the lobe structure of the transmittingradar system's antenna pattern. If the transmitting radar system'stransmitter is not blanked, the fly-back may be observed (e.g., viaaudio cues to an operator). The envelope of the unidirectional sectorscan is similar to the envelope of the circular scan except that theenvelope of the unidirectional sector scan does not show the back lobestructure.

[0035]FIG. 1G is a time domain plot of the envelope of a bi-directionalsector scan. A bi-directional sector scan is a continuousone-dimensional scan in azimuth resulting in modulation of the receivedcarrier frequency displaying the lobe structure of the transmittingradar system's antenna pattern. The scan periods in each direction aretypically of different length, thus distinguishing the bi-directionalsector scan envelope from the circular scan envelope. However, if thereceiving platform is located on a ray bifurcating of the transmittingradar's scan axis, the bi-directional sector scan may beindistinguishable from the unidirectional sector scan envelope.

[0036]FIG. 1H is a time domain plot of the envelope of a circular rasterscan. A circular raster scan is a two-dimensional scan in azimuth andelevation defined as a slow circular scan in azimuth with a fasterunidirectional superimposed elevation sector scan (thus not a trueinterlaced raster). From the perspective of the receiving platform, theenvelope of the circular raster scan appears similar to the envelope ofthe helical scan. However, audio cues provided by the envelope of thecircular raster scan differ substantially from audio cues provided bythe envelope of the helical scan. The difference is based, primarily onthe modulation rates associated with each scan type. The main lobes of acircular raster scan are separated at the elevation scan period, and notthe azimuth scan period as in the helical scan. Also, the elevation scanrate for the circular raster scan is greater than the azimuth scan ratefor helical scan.

[0037]FIG. 1I is a time domain plot of the envelope of a unidirectionalraster scan. A unidirectional raster scan is a two dimensional scancomprising a unidirectional sector scan in azimuth superimposed on aslower unidirectional sector scan in elevation (thus, not a true rasterscan). From the perspective of the receiving platform, the envelope ofthe unidirectional raster scan appears similar to the envelope of thehelical and circular raster scans. However, audio cues provided by theenvelope of the unidirectional raster scan differ substantially fromaudio cues provided by the envelope of the helical and circular rasterscans. The difference is based, primarily on the modulation ratesassociated with each scan type. The main lobes of a unidirectionalraster scan are separated at the elevation scan period, and not theazimuth scan period as in the helical scan. Also, the elevation scanrate for the unidirectional raster scan is greater than the azimuth scanrate for helical scan.

[0038]FIG. 1J is a time domain plot of the envelope of a bi-directionalraster scan. A bi-directional raster scan is a two dimensional scancomprising a bi-directional sector scan in azimuth superimposed on aslower unidirectional sector scan in elevation (thus, not a trueinterlaced raster scan). From the perspective of the receiving platform,the scan envelope appears similar to a unidirectional raster scan,except that alternating scan periods differ. However, if the receivingplatform is located on a ray bifurcating the scan axis, thebi-directional raster scan appears very similar to the unidirectionalraster scan.

[0039]FIG. 1K is a time domain plot of the envelope of a spiral scan. Aspiral scan is a two dimensional scan in azimuth and elevation. From theperspective of the receiving platform, the envelope of the spiral scanappears similar to a conical scan in azimuth combined with a lowerfrequency (scan frequency) conical scan in elevation.

[0040]FIG. 1L is a time domain plot of the envelope of a Palmer circularscan. A Palmer circular scan is defined as a slower circular scan (inazimuth) having a higher rate conical scan superimposed upon it.

[0041]FIG. 1M is a time domain plot of the envelope of Palmerunidirectional scan. A Palmer unidirectional scan is defined as a slowerrate unidirectional sector scan having a higher rate conical scansuperimposed upon it.

[0042]FIG. 1N is a time domain plot of the envelope of Palmerbi-directional scan. A Palmer bi-directional scan is defined as a slowerrate bi-directional sector scan having a higher rate conical scansuperimposed upon it.

[0043]FIG. 1P is a time domain plot of the envelope of a true rasterscan. A true raster scan is a two dimensional scan in azimuth andelevation resulting in an envelope comprising interlaced elevationsteps. The envelope of a true raster scan in not monotonic. From theperspective of the receiving platform, the modulation appears to besimilar to a vertical sector scan, wherein the average received signalstrength exhibits interlaced steps. The average received signal strengthgenerally (not monotonically) increases as the transmitting radarsystem's mainlobe beam approaches the elevation of the receivingplatform. The average received signal strength generally (notmonotonically) decreases as the transmitting radar system's mainlobebeam moves away from the receiving platform's elevation. The maximumsignal strength of the received energy is observed at the scan sweepclosest to the receiving platform's elevation. The maximum signalstrength slowly increases as the azimuth scan approaches the receivingplatform's position, and slowly decreases as the azimuth scan moves awayfrom the receiving platform's position.

[0044]FIG. 1Q is a time domain plot of the envelope of a Palmer rasterscan. A Palmer raster scan comprises a higher rate conical scansuperimposed upon a slower rate true raster scan.

[0045]FIG. 2 is a functional block diagram of an exemplary automaticscan type recognition system 200 in accordance with the presentinvention. As shown, a signal is received by scan detector 22. Thesignal received by scan detector 22 may be in various forms, includingelectromagnetic, acoustic, and optical. In an exemplary embodiment ofthe invention, the signal received by scan detector 22 is a radarsignal. Scan detector 22 receives the radar signal and provides anenvelope signal 23, representing the scan type of the received signal,to the transformer 24. The scan detector 22 may comprise any type ofenvelope detector circuit, such as a diode, a capacitor, and a resistorfor detecting the shape of the input envelope of the Radar signal andgenerating an output voltage waveform corresponding to the envelope ofthe input Radar Signal, for example. The transformer 24 transforms theenvelope signal from the time domain to the frequency domain. Thefrequency domain signal is provided to optional integrator 32, to beintegrated, or averaged, over a predetermined time period or number ofscans. The integrated signal 33, is provided to correlator 34 which alsoreceives as input scan data 38. Correlator 34 compares integrated signaldata 33 with the predetermined sets of scan data 38 to generate anoutput signal 35. The resultant output signal 35 provided by thecomparison process are evaluated by decision block 36 for providing anindicator of the scan type of the received signal.

[0046]FIG. 3 is a functional block diagram of an exemplary scan detectorin accordance with an embodiment of the present invention. In thisembodiment, scan detector 22 comprises a receiver 26, an envelopedetector 28, and an analog to digital (A/D) converter 30. Receiver 26 isa transducer, which receives the radar signal and converts it to anelectrical signal. Receiver 26 may be any appropriate receiver known inthe art such as a detector diode and integrator, for example. Envelopedetector 28 receives the electrical signal provided by receiver 22 anddemodulates the signal, providing the envelope of the scan of thesignal. The envelope signal is provided to the A/D converter 30 forconversion from an analog signal to a digital signal. A/D converter 30is optional. An automatic scan recognition system in accordance with thepresent invention may comprise analog and/or digital processing.However, a plethora of software and algorithms have been developed fordigital processors with applications for digital signals. thus in anexemplary embodiment of the invention, the analog envelope signal isconverted to a digital envelope signal by A/D converter 30.

[0047] Referring again to FIG. 2, the scan detector 22 provides anenvelope signal to the transformer 24. The transformer 24 transforms theenvelope signal in the time domain to the frequency domain. Thetransformer 24 performs any type of appropriate transformation such as aFourier transform or a Laplace transform. The transformer 24 may performthe transformation on either an analog or digital signal. Examples ofalgorithms used to perform the transformation of a digital version ofthe envelope signal in accordance with an exemplary embodiment of theinvention include the Fast Fourier Transform (FFT) and the DiscreteFourier Transform (DFT). In an exemplary embodiment of the invention,the digital transformed envelope is stored in memory in the form ofFourier coefficients. The Fourier coefficients represent the amplitudeof each frequency bin of the digitized envelope signal. The transformer24 provides the transformed envelope signal to the optional integrator32.

[0048] The integrator 32 combines a plurality of received scans into asingle scan. The integrator 32 combines these scans to improveprocessing performance by, for example, decreasing noise, increasing thesignal to noise ratio, and/or reducing processing throughputrequirements. Combining scans with integrator 32 is optional. If thereceived scans differ from scan to scan, integration (combination) maynot improve processing performance. Thus, various embodiments of theinvention may or may not comprise integrator 32. In yet anotherembodiment of the invention, integration is accomplished in the timedomain, before performing a time domain to frequency domaintransformation. Integrator 32 may perform any appropriate type ofcombination including, for example, a straight summation, a weightedsummation, an average, a weighted average, and an integration function.

[0049] The frequency domain data of the envelope signal (e.g., Fouriercoefficients) are compared to predetermined sets of scan data 38 bycorrelator 34. Each predetermined set of scan data comprises frequencydomain data representing a particular scan type. In an exemplaryembodiment of the invention, each predetermined set of scan datacomprises Fourier coefficients representing each of the scan typesdescribed herein with respect to FIGS. 1A through 1Q. The comparisonprocess may comprise any appropriate comparison process, such as a datapoint to data point comparison, and/or a cross-correlation process.Also, the cross-correlation process may comprise applying windowing, ortapering, functions (windowing and tapering functions are well know inthe art) to the frequency domain envelope signal, the data set, or both.Further, to increase the probability of correct scan typeidentification, the comparison process may comprise squaring or cubingeach frequency bin of the frequency domain envelope signal, the dataset, or both. The squaring/cubing process may be done prior to, orafter, the actual comparison of the data.

[0050] The results of the comparison process performed by correlator 34are analyzed in the decision block 36. Decision block 36 analyzes theresults of the comparison to determine the degree of similarity betweenthe frequency domain representation of the envelope signal and thepredetermined sets of scan data 38. If a desired degree of similarity ismet between the frequency domain of the envelope signal and apredetermined set of scan data, the scan type of the received signal isdetermined to be of the type represented by that data set. For example,assume a signal is received by scan detector 22 and processed inaccordance with an FFT algorithm by transformer 24. Fourier coefficientsof the received signal are then compared to several sets of data 38 inaccordance with a cross-correlation function by correlator 24. Assumingfurther that the output for each cross-correlation, except one, isapproximately equal to 0.1, and one cross-correlation is equal to 0.9.Decision block 36 will determine that the scan type represented by thedata set that resulted in 0.9 to be the scan type of the receivedsignal. Accordingly, this scan type will be provided to an operator,display device, storage device, and/or a processor.

[0051] Decision block 36 may determine if the desired degree ofsimilarity is met in any of several ways. For example, the desireddegree of similarity may be considered met by all comparison resultsabove a predetermined threshold, by the comparison result with thehighest result value above a predetermined threshold, and/or by thecomparison result (or results in the case of a tie) with the highestresult value from all comparison results. To further increase theprobability of correctly determining a received scan type, adiscrimination function may be applied to the comparison and decisionprocesses.

[0052]FIG. 4 is a flow diagram of an exemplary process to automaticallydetermine a scan type in accordance with an embodiment of the invention.In step 42, a signal is received and processed as described herein withreference to scan detector 22. The received signal may be in variousforms, including electromagnetic, acoustic, and optical. In an exemplaryembodiment of the invention, the received signal is a radar signal.Envelope detection is performed in step 44. An envelope signal,representing the scan type of the received signal is developed. Theenvelope of the received signal is transformed from the time domain tothe frequency domain in step 46, in accordance with the descriptionprovided herein with reference to transformer 24. Appropriatetransformations include a Fourier transform or a Laplace transform.Transformation may be performed on either an analog or digital signal.Examples of algorithms used to perform the transformation of a digitalversion of the envelope signal in accordance with an exemplaryembodiment of the invention include the Fast Fourier Transform (FFT) andthe Discrete Fourier Transform (DFT). In an exemplary embodiment of theinvention, the digital transformed envelope is by Fourier coefficients.The Fourier coefficients represent the amplitude of each frequency binof the digitized envelope signal. The frequency domain signal may beoptionally integrated, as described herein with reference to integrator32.

[0053] The frequency domain signal is compared with predetermined setsof scan data in step 48. The results of the comparison process areevaluated and a determination as to the scan type of the received signalis performed in step 50. The comparison process (step 48) and decisionprocess (step 50) are performed in accordance with the descriptionprovided herein with reference to correlator 34, decision block 36, andscan data 38. The frequency domain data of the envelope signal (e.g.,Fourier coefficients) are compared to predetermined sets of scan data,wherein each predetermined set of scan data comprises frequency domaindata representing a particular scan type. In an exemplary embodiment ofthe invention, each predetermined set of scan data comprises Fouriercoefficients representing each of the scan types described herein withrespect to FIGS. 1A through 1Q. The comparison process (step 48) maycomprise any appropriate comparison process, such as a data point todata point comparison, and/or a cross-correlation process. Further, toincrease the probability of correct scan type identification, thecomparison process (step 48) may comprise squaring or cubing eachfrequency bin of the frequency domain envelope signal, each scan dataset, or both. The squaring/cubing process may be done prior to, orafter, the actual comparison of the data.

[0054] The results of the comparison process (step 48) are analyzed instep 50 to determine the degree of similarity between the frequencydomain representation of the envelope signal and the predetermined setsof scan data. If a desired degree of similarity is met between thefrequency domain of the envelope signal and a predetermined set of scandata, the scan type of the received signal is determined to be of thetype represented by that data set. The determined scan type is providedto an operator, display device, storage device, and/or a processor. Adesired degree of similarity may be considered met by performing any ofseveral techniques. For example, the desired degree of similarity may beconsidered met by all comparison results above a predeterminedthreshold, by the comparison result with the highest result value abovea predetermined threshold, and/or by the comparison result (or resultsin the case of a tie) with the highest result value from all comparisonresults. To further increase the probability of correctly determining areceived scan type, a discrimination function may be applied to thecomparison process (step 48) and/or the decision process (step 50).

[0055] The present invention may be embodied in the form ofcomputer-implemented processes and apparatus for practicing thoseprocesses. FIG. 5 is a block diagram of a receiving platform comprisingan antenna 60 and a computer processor 62, in accordance with anexemplary embodiment of the invention. A signal is received by antenna60. Antenna 60 may be any antenna known in the art, typically designedto intercept radar signals of various polarizations over a widefrequency range, such as a horn antenna, a parabolic dish antenna,and/or an antenna array (all with circularly polarized or dualorthogonal linearly polarized feeds or elements). Envelope detection,transformation, comparison, and decision processes are performed, asdescribed herein, by the computer processor 62. Processing may also beperformed by special purpose hardware.

[0056] The present invention may also be embodied in the form ofcomputer program code embodied in tangible media, such as floppydiskettes, read only memories (ROMs), CD-ROMs, hard drives, high densitydisk, or any other computer-readable storage medium, wherein, when thecomputer program code is loaded into and executed by computer processor62, the computer processor 62 becomes an apparatus for practicing theinvention. The present invention may also be embodied in the form ofcomputer program code, for example, whether stored in a storage medium,loaded into and/or executed by computer processor 62, or transmittedover some transmission medium, such as over electrical wiring orcabling, through fiber optics, or via electromagnetic radiation,wherein, when the computer program code is loaded into and executed bycomputer processor 62, the computer processor 62 becomes an apparatusfor practicing the invention. When implemented on a general-purposeprocessor, the computer program code segments configure the processor tocreate specific logic circuits.

[0057] Although illustrated and described herein with reference tocertain specific embodiments, the present invention is nevertheless notintended to be limited to the details shown. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the spirit of theinvention.

What is claimed is:
 1. A method for determining a scan type of a signal,said method comprising: receiving a signal associated with a given scantype; performing scan detection on said signal for providing an envelopesignal, said envelope signal being indicative of said received scantype; transforming said envelope signal; comparing said transformedenvelope signal with at least one predetermined data set, each data setcorresponding to one of a plurality of predetermined scan types; anddetermining the scan type of said signal in accordance with a degree ofsimilarity of said at least one predetermined data set and saidtransformed envelope signal.
 2. A method in accordance with claim 1,wherein said scan type is indicative of a transmission amplitudemodulation characteristic of said signal.
 3. A method in accordance withclaim 1, wherein said envelope signal is transformed from a time domainsignal to a frequency domain signal.
 4. A method in accordance withclaim 1, wherein said transformation comprises one of a Fouriertransform, a Laplace transform, an FFT, and a DFT.
 5. A method inaccordance with claim 1, wherein said signal comprises one ofelectromagnetic energy, acoustic energy, and optical energy.
 6. A methodin accordance with claim 1, wherein said received signal represents aradar signal.
 7. A method in accordance with claim 1, wherein said stepof comparing said transformed envelope signal with at least onepredetermined data set comprises cross-correlating said transformedenvelope signal with at least one predetermined data set.
 8. A method inaccordance with claim 1, wherein a scan type of said signal isdetermined to be a scan type corresponding to a compared data set ifsaid degree of similarity exceeds a predetermined threshold.
 9. A systemfor determining a scan type of a signal, said system comprising: a scandetector for receiving said signal and providing an envelope signal,said envelope signal being indicative of said a scan type of saidsignal; a transformer for transforming said envelope signal; acorrelator for comparing said transformed envelope signal with at leastone predetermined data set, wherein each predetermined data setcorresponds to one of a plurality of scan types; and; a decision blockfor determining the scan type of said signal in accordance with a degreeof similarity of said at least one predetermined data set and saidtransformed envelope signal.
 10. A system in accordance with claim 9,wherein said transformer comprises one of a Fourier transformer, aLaplace transformer, an fast Fourier transformer, and a discrete Fouriertransformer.
 11. A system in accordance with claim 9, wherein saidreceived signal represents a radar signal.
 12. A system in accordancewith claim 9, wherein said correlator comprises a cross-correlator forcross-correlating said transformed envelope signal with at least onepredetermined data set.
 13. A system in accordance with claim 9, whereina scan type of said signal is determined to be a scan type correspondingto a compared data set if said degree of similarity exceeds apredetermined threshold.
 14. A system in accordance with claim 9,wherein said scan type is indicative of a transmission amplitudemodulation characteristic of said signal.
 15. A computer readable mediumhaving embodied thereon a computer program for causing a computer todetermine a scan type of a signal, the computer readable programcomprising: means for causing said computer to perform scan detection onsaid signal for providing an envelope signal, said envelope signal beingindicative of said scan type of said signal; means for causing saidcomputer to transform said envelope signal; means for causing saidcomputer to compare said transformed envelope signal with at least onepredetermined data set, wherein each predetermined data set correspondsto one of a plurality of scan types; and means for causing said computerto determine the scan type of said signal in accordance with a degree ofsimilarity of said at least one predetermined data set and saidtransformed envelope signal.
 16. A computer readable medium inaccordance with claim 15, wherein said computer program comprises meansfor causing said computer to transform said envelope signal inaccordance with one of a Fourier transform, a Laplace transform, an FFT,and a DFT.
 17. A computer readable medium in accordance with claim 15,wherein said signal represents a radar signal.
 18. A computer readablemedium in accordance with claim 15, wherein said computer programcomprises means for causing said computer to cross-correlate saidtransformed envelope signal with at least one predetermined data set.19. A computer readable medium in accordance with claim 15, saidcomputer program comprises means for causing said computer to determinethat a scan type of said signal is a scan type corresponding to acompared data set if said degree of similarity exceeds a predeterminedthreshold.
 20. A computer readable medium in accordance with claim 15,wherein said scan type is indicative of a transmission amplitudemodulation characteristic of said signal.